Fuel cell anode structures for voltage reversal tolerance

Abstract

In a solid polymer fuel cell series, various circumstances can result in a fuel cell being driven into voltage reversal by other cells in the series stack. For instance, cell voltage reversal can occur if that cell receives an inadequate supply of fuel (for example, fuel starvation). In order to pass current during fuel starvation, reactions other than fuel oxidation may take place at the fuel cell anode, including water electrolysis and oxidation of anode components. The latter may result in significant degradation of the anode. Such fuel cells can be made more tolerant to cell reversal by promoting water electrolysis over anode component oxidation at the anode. This can be accomplished by enhancing the presence of water in the anode catalyst layer through modifications to the anode structure or anode composition near or in the catalyst layer. For instance, water electrolysis during voltage reversal is promoted through the use of different or additional ionomer, polytetrafluoroethylene, or graphite in the anode catalyst layer, or through the use of certain sublayers between the anode catalyst layer and the anode substrate.

What is claimed is:  
     
       1. A method of making a solid polymer electrolyte fuel cell more tolerant to voltage reversal, said fuel cell comprising a cathode, a solid polymer electrolyte, and an anode, and said anode comprising an anode substrate and an anode catalyst layer located between said substrate and said solid polymer electrolyte, wherein said method comprises decreasing the flow of water through said anode catalyst layer to said anode substrate, wherein said water flow is decreased by incorporating a porosity-reducing additive in said anode catalyst layer, wherein said porosity reducing additive occupies from about 0.1 to 0.2 μl volume per cm 2  of said anode catalyst layer. 
     
     
       2. The method of  claim 1  wherein said porosity reducing additive comprises a mixture of polytetrafluoroethylene and acetylene carbon black. 
     
     
       3. The method of  claim 1  wherein said anode catalyst layer comprises between about 12% and 32% by weight of polytetrafluoroethylene. 
     
     
       4. The method of  claim 1  wherein said anode catalyst layer comprises between about 0.03 and 0.2 mg/cm 2  of acetylene carbon black. 
     
     
       5. A method of making a solid polymer electrolyte fuel cell more tolerant to voltage reversal, said fuel cell comprising a cathode, a solid polymer electrolyte, and an anode, and said anode comprising an anode substrate and an anode catalyst layer located between said substrate and said solid polymer electrolyte, wherein said method comprises decreasing the flow of water through said anode catalyst layer to said anode substrate, wherein said water flow is decreased by incorporating a sublayer between said anode catalyst layer and said substrate. 
     
     
       6. The method of  claim 5  wherein said sublayer comprises graphite. 
     
     
       7. The method of  claim 5  wherein said sublayer comprises Ti 4 O 7 . 
     
     
       8. A method of making a solid polymer electrolyte fuel cell more tolerant to voltage reversal, said fuel cell comprising a cathode, a solid polymer electrolyte, and an anode, and said anode comprising an anode substrate and an anode catalyst layer located between said substrate and said solid polymer electrolyte, wherein said method comprises increasing the water content in said anode catalyst layer, said method comprising increasing the water content in said anode catalyst layer to an amount greater than that contained in a layer comprising 30% by weight amount of fully hydrated perfluorosulfonic ionomer with 1100 equivalent weight and no other additives. 
     
     
       9. A method of making a solid polymer electrolyte fuel cell more tolerant to voltage reversal, said fuel cell comprising a cathode, a solid polymer electrolyte, and an anode, and said anode comprising an anode substrate and an anode catalyst layer located between said substrate and said solid polymer electrolyte, wherein said method comprises increasing the water content in said anode catalyst layer, wherein said water content is increased by incorporating a hygroscopic additive in said anode catalyst layer, wherein said hygroscopic additive is graphite. 
     
     
       10. A solid polymer electrolyte fuel cell with improved voltage reversal tolerance, said fuel cell comprising a cathode, a solid polymer electrolyte, and an anode, and said anode comprising an anode substrate and an anode catalyst layer located between said substrate and said solid polymer electrolyte, wherein said anode catalyst layer comprises between about 6% and about 32% polytetrafluoroethylene and between about 0.03 mg/cm 2  and about 0.2 mg/cm 2  of acetylene carbon black. 
     
     
       11. The fuel cell of  claim 10  wherein said anode catalyst layer comprises between about 12% and 29% by weight of polytetrafluoroethylene and between about 0.03 mg/cm 2  and about 0.2 mg/cm 2  of acetylene carbon black. 
     
     
       12. A solid polymer electrolyte fuel cell with improved voltage reversal tolerance, said fuel cell comprising a cathode, a solid polymer electrolyte, and an anode, and said anode comprising an anode substrate and an anode catalyst layer located between said substrate and said solid polymer electrolyte, wherein said anode catalyst layer comprises an uncatalyzed acetylene carbon black additive. 
     
     
       13. The fuel cell of  claim 12  wherein said anode catalyst layer comprises between about 0.03 and 0.2 mg/cm 2  of said uncatalyzed acetylene carbon black additive. 
     
     
       14. A solid polymer electrolyte fuel cell with improved voltage reversal tolerance, said fuel cell comprising a cathode, a solid polymer electrolyte, and an anode, and said anode comprising an anode substrate, an anode catalyst layer located between said substrate and said solid polymer electrolyte and a sublayer located between said anode catalyst layer and said substrate, wherein said sublayer comprises graphite or Ti 4 O 7 . 
     
     
       15. A solid polymer electrolyte fuel cell with improved voltage reversal tolerance, said fuel cell comprising a cathode, a solid polymer electrolyte, and an anode, and said anode comprising an anode substrate and an anode catalyst layer located between said substrate and said solid polymer electrolyte, wherein said anode catalyst layer comprises a catalyst and a carbon material that does not support said catalyst. 
     
     
       16. The fuel cell of  claim 15  wherein said carbon material comprises between about 0.03 and 0.2 mg/cm 2  of acetylene carbon black.